Variable resistor for dual operation

ABSTRACT

A variable resistor providing an integral assembly for dual operation comprising a pair of arcuate resistance track elements in axially spaced, face-to-face relationship and having interposed therebetween a single insulating rotor or brush carrier including oppositely facing cavities, each cavity being recessed relative to a central plane and adapted to individually receive conducting brush members. Biasing springs are provided for maintaining the brush members in electrical contact with the respective resistance elements, as well as individual terminal assemblies for each of the resistance elements.

United States Patent inventor Appl. No. Filed Patented Assignee VARIABLERESISTOR FOR DUAL OPERATION 7 Claims, 4 Drawing Figs.

Primary Examiner-Lewis H. Myers Assistant Examiner-Gerald P. TolinAttorneys-Arnold J. Ericson and Richard C. Steinmetz, Jr.

ABSTRACT:. A variable resistor providing an integral as- U.S.Cl 338/170,sembly for dual operation comprising a i f arcuate 338/132 338/164!338/167, 338/174 338/202 sistance track elements in axially spaced,face-to-face relall'llt. tion hi and having interposed therebetween asingle insulat. Field of Search 338/ 128, ing rotor or b h can'ierincluding oppositely facing cavities, 130, 132, 162, 164, 166, 167, 170,171, 174, 184, each cavity being recessed relative to a central planeand 202, 230 adapted to individually receive conducting brush members.Biasing springs are provided for maintaining the brush mem- Referencescued bers in electrical contact with the respective resistance ele-UNITED STATES PATENTS ments, as well as individual terminal assembliesfor each of the 2,111,810 3/1958 Schellenger 201/55 resistance elements.

45 47 25 2+ 3 |5 23 H 43 46 Y Y |7 36 24 i 30 22 I f I) 37 I 26 42 39 2+II 3| 4 T 0 2| BACKGROUND OF THE INVENTION The present invention relatesto mechanically variable resistors having movable contacts electricallyadjustable over a length of resistance element, and in particular to avariable resistor wherein there is a pair of such resistance elements inaxially spaced, facing relationship and including respective movablecontacts for each of the elements actuated by a single rotor, and inwhich all of the components are enclosed in a single, housing.

Components of the nature disclosed herein have in the past been mountedin tandem arrangement with individual movable contact elementselectrically engaging separate resistance elements. The movable contactelements were attached in axially spaced relationship along a commonoperating shaft. This made for relatively long and cumbersomeconstructions.

There have also been some attempts to combine the contacts in a singlerotor, but these contacts were generally of leaf spring constructionwith the contact buttons being made an integral part of the distal endof the lead spring and verymuch dependent upon variations in the springmaterial, length of spring and other factors influencing the toleranceof the construction.

SUMMARY or TIIE INVENTION device that will readily adapt itself to suchapplications asbridged T- and L-attenuators which require in theirconstruction the obtainment of a specified resistance impedance in theoperation of dual variable resistance. It is further important that theimpedance relationship be maintainedthroughout the range of resistancevalues as the device is operated. The manner of construction of thepresent device provides a positive attainment of such impedancerelationship, independent of the variations normally found in leafspring contact constructions.

The present invention, in its preferred embodiment, adapts certain ofthe features of the Variable Resistance Device disclosed in US. Pat. No.2,839,642 granted to the present inventor jointly with Bernard F.Tellkamp and assigned to the same assignee as the present invention.That is, the embodiment may utilize integrally molded resistor elementssuch as those set forth in the US. Pat. Nos. 2,269,136 and 2,514,682 toTellkamp. However, it is contemplated that the construction of teeresistance elements may take other forms such as conventional cermet orthick film resistance tracks, as well as other resistance tracks wellknown in the art.

The resistance elements each provide an arcuate track which may be ofconstant resistance throughout its length or variable, as desired, andin the case of otentiometers, a centrally disposed collector track ofconducting, low-resistance material. The resistance elements areretained in axially spaced, face-to-face relationship by means of atubular enclosure or casing. An operating shaft protrudes through acentral aperture of one of the resistance elements and has attached toits internal end portion an insulating rotor elementincluding twooppositely disposed cavities recessed inwardly relative to a centralplane dividing the rotor perpendicularly of its axis. Within each of thecavities there is located a conducting brush which is rotatable with therotor about an axis substantially concentric with the respectiveresistance tracks and having collector engaging portions in slidingcontact with the collector track and a resistance engaging portion insliding contact with the resistance track. Relatively flat springelements are seated in the respective cavities to bias the brushesoutwardly of the cavities and towards their respective resistanceelements.

It is therefore among the objects of the present invention to provide avariable resistor of diminutive size which includes among its variousfeatures the provision of well proven and commercially acceptedresistance elements and brush constructions and which combine all ofthese features in the device to provide a dual functioning, variableresistor enclosed within a single housing to thereby reduce both itsradial and axial length when compared to conventional tandem operatedvariable resistors.

BRIEF DESCRIPTION OF THE DRAWING The attached drawing, which comprises apart hereof, discloses the invention, as follows:

FIG. 1 is a longitudinal view, partially in section, of a variableresistor in the form of a potentiometer incorporating the teachings ofthe present invention;

FIG. 2 is a cross-sectional view taken along lines 2-2 of FIG. 1 andillustrating, more particularly, a construction of the rotor or brushcarrier;

FIG. 3 is a cross-sectional view taken along lines 3-3 of FIG. I, andillustrates the configuration of the resistance track and collectortrack as used in the dual resistance elements; and

FIG. 4 is an enlarged fragmentary view of another embodiment of thebrush construction.

DESCRIPTION OF THE FREE ERRED EMBODIMENTS Referring now to the drawing,and in particular to the views of FIGS. l3, there is shown a resistanceelement in the form of a molded base 10 of insulating material. The base10 provides a surface 11 preferably of circular configuration. Theconfiguration of the resistance and collector tracks of the surface 11is similar to the interior surface 12 of an axially spaced resistanceelement 13, except for a rotative positioning relative to thelongitudinal plane of the device for purposes hereinafter described.Attention is directed to'FlG. 3 which more clearly shows theconfiguration of the surface 12 of the element 13. Embedded within thebase 10 and the element 13, and exposed flush with the respective faces11 and 12, are circular resistance tracks 14 and 15, respectively, eachin the form of a nearly completed ring. The tracks 14,15 each comprise ashallow layer of conducting material in the form of distributedcarbon-black particles dispersed within the molded material of therespective base 10 and element 13 to have become an integral portionthereof upon molding. Substantially concentric with the resistancetracks 14, 15 are respective collector tracks 16 and 17, also exposedfiush with the respective faces 11 and 12. The tracks 16, 17 cover acircular area at the center of the respective faces 11 and 12 and, likethe tracks 14, 15 are formed of a plurality of conducting particlesmolded integrally with the respective base 10 and element 13 in ashallow layer near the surface. The particles comprising the collectortracks 16, 17 are more densely distributed only rather than apotentiometer, in the form of thick film or cermet surfaces as is wellknown in the art.

Returning to the description of the base 10, a set of threeterminalleads 20 (one of them not being shown) are embedded within the base 10at the time of molding and there disposed with the embedded end of onein electrical contact with the collector track 16 and the embedded endsof the others in contact with the end portions of the resistance track i14. The terminals 20 are shown in longitudinal projection The terminals21 of the element '13 are molded in {place in similar manner toterminals 20, and project downwardly relative to FIG. 1. Should it bedesired to provide the aforementioned means for including downwardlyprojecting terminals 20, the setsof terminals 20,21 will be chosendimensionally to fit into known circuit board constructions.

- Both the molded base 10 and the resistance element 13 also haveembedded therein metallic heat extracting and housing anchoring inserts22 and 23, preferably composed of a :metal having high heatconductivity. The inserts are more clearly shown and described in detailin the Dickinson et al. US. Pat. No. 2,839,642. They generally take theform of an interrupted cylinder with a plurality of perforations throughwhich the material of the-base 10 and theelement 13 may flow, uponmolding, to rigidly secure the inserts 22, 23. Each of the in serts 22,23 with its respective forward edge 24, 25 behind, spaced from but very,near the respective resistance tracks 14, 15, as shown in FIG. 1, toreadily receive heat released within the resistance tracks l4, 15 and toconduct the same to the exterior of the'base 10 and resistance element13.

' The base 10 and resistance element 13 are retained in axially spacedrelationship by means of a housing or casing-26 which is preferably of ametallic heat-conducting material. At the bottom of the housing, asviewed in FIG. 1, it will be noted that'a portion of the housing islanced inwardly from its right end withtheseparated portion bentinwardly to formya rotor stop as will. be Iaterdescribed. Thecasing'26'is provided'with a set of ears (not shown) which act to retaina threaded bushing 30 having a circular base 31 resting against theresistance elenient 13.v The free ends of the aforementionedears arebent over the bushing base 31 to secure the bushing 30 in position.Extending through the bushing 30 is an operating shaft-32 hav ing areduced cross section33 and a'knurled end 34 withirijthe casing '26. Theknurled end 34 and the reduced portion 33 are embedded within a'moldedcontact carrier or rotor 35 composed of an insulating material. Therotor is provided with a projecting molded portion 39 which acts toinsulate the shaft 32 -from the collector ring 17 in additiontojproviding a "bearingsurface for thero'tor 35. The bushing 30 isrecessed at 36 to receive an -O-rin'g gasket 37 which is compressedbetween the interior circular wall of the recessed cavity 36 and theshaft 32 to provide a seal. The brush carrier or rotor 35 is slotted at38 for purposes of assembly in order to clear the inwardly foldedportion 27 of the casing. Although not shown, the rotor'35 is molded'toproyide a projection which will engage either side of the portion 2 7for purposes of limiting rotation thereof. The movement of of a novelmodification of the brush carrier or rotor 35 to permit this dualfunction. That is, the brush carrier 35 is recessed to providediametrically opposed cavities 40 :for respectively receivingelectrically conducting brushes 42 and 43 of carbon and the respectivepair of biased springs 44 and 45. With reference to FIGS. 1 and 2, itwill be noted that each of the brushes has a substantially identicalconfiguration, the rear- I ward side of brush 43 and the forward side ofbrush 42 being shown in the cross-sectional view of FIG. 2. As viewedinFIG. l5and 2, itwill be noted that the brush carrier 35 is provided withan arcuate protruding portion 46 which acts as a stop for the rotor 35on any endward, axial thrust being placed upon the shaft 32 duringadjustment. That is, the rotor 35 will in no way touch theresistance'track 15 or the collector track 17 as the *protruding'portion46 is disposed to rest against the inner 'face 11 of the base 10intermediate the said tracksl5 and 17.

Each of the brushes 42,43 are of general 'triangular'configuration to berespectively seated in the generally triangular configured recesses 40and 4-1 of the rotor 35, respectively. As shown in FIG. 2 and asparticularly'illustrated with regard to brush 42, each of the brushes 42,43 are provided with three 'co ntacttoes47, 48 and 49. The tworadially inwardly disposed toes 48, 49 rest upon and electrically engagethe respective collector tracks 10 and 17 of the baselfl'and theresistance element 13. whereas the outwardly positioned toe 47'ridesupon and electrically engages the resistance-tracks 14 and 15. Thetriangular disposition and spacingtofthe toes 47, 48 and 49'alsoprovides stability for the respective brushes 42, 43.

As shown on FIG. 2, the springs 44, are disposed in laterally projectingrecessed portions of the cavities 40 and 41. The laterally projectingrecesses are formed with abutments at their extremities 50 to receivethe ends of the respective springs 44,45. The intermediate portion'ofeach of the springs 44, 45 bears againstthe angled back surface 51 ofthe respective brushes 42,43 and is bowed to'provide necessary contactpressure between-the brush toes 47 and the exposed surface areas of thetracks 14, 1'5 and 16, 17. It will be further observed that the forceexerted by the springs 44, 45 against the angled back surface'SI'dividesinto two components,-one biasing the respective brush 42, 43 towards therespective faces 11 and 12, and the other force component biasing therespective brush in adirection towards the forward surface defining thetoe 47. The latter-component acts to retain the brush'in its cavity,which is especially helpful during assembly of the device. The use of aplurality of springs 44, 45permitscontacting engagement-with the angledbacksurface 51 of the brush'to provide a spring characteristic similarto that of a flat spring.

It will be apparent from the above description that manual rotation ofthe shaft 32 willcause the rotor 35 molded to the inward endof the shaftto rotationally move the conducting brushes 42 and 43 circumferentiallyof the concentric resistance and'colle'ctor tracks 14, 1'6 and 15 17,respectively. This dual operation is performed in a minimum axialdimension between the resistance elements 10 and 13 by seating therespective brushes-42 and 43in cavities 40 and '41 which are disposedinwardly of aplane cross-sectionally bisecting the ro- FIG. 4 isillustrative'of another brush embodiment, and like parts are describedby referring to like numerals. As stated above,'the springs .44, 45 bearagainst the angled back surface 51 of the brushes 42, 43. Thisarrangement provides desired contact pressure between the toe 47 and therespective resistor track 14, 15. However, such arrangement also tendsto wedge the apex forming the outer surface of the toe 47 of thetriangular brush against the mating surface of the triangular recess ofthe rotor 35.

In order to minimize the wedging condition and thereby permit freedomofbrushaction when the rotor is operated, the surface of the recessengaging the toe 47 is preferably formed as shown in FIG. 4. That is,the apex is further defined by the planar surface portions 52iand 53,which lie in angular planes intersecting at the-terminus of the apex.This provides a two point" contact for the rounded toe 47. The brush 43(shown in FIG. 4) and the brush 42 will then be assured freedom ofmovement in the recess 41 of the rotor 35 even under bias of therespective springs 45,-44.

I claim: 1. A variable resistance apparatus comprising: a housing; J I apair of spaced-apart, stationary insulating substrate element supportedby said housing, at least one of which includes'ashaft-receivingaperture; an arcuate resistance track and a conductingcollector track supported by each of said substrate elements and inrespective facing relationship;

a rotatable shaft received in the apertured substrate element andextending inwardly of said housing;

an integrally formed insulated contact brush carrier supported on theinner end of said rotatable shaft and positioned intermediate saidresistance elements, said contact brush carrier containing a pair ofreentrant brush-receiving cavities on opposite sides thereof anddisposed'angularly relative to one another, the operi ends of saidcavities facing respective resistance tracks and collector trackssupported by the respective substrate elements, the said reentrantcavities of said brush carrier each having a depth exceeding one-halfthe axial length of said brush carrier;

conducting contact brushes disposed on opposite sides of said contactcarrier and positioned in the respective cavities of said contact brushcarrier and slidably electrically bridging the respective facingresistance and collector tracks;

biasing means at opposite sides of said contact carrier disposed in saidrespective cavities intermediate a respective inner end of said cavitiesand its respective brush, thereby biasing said brush into electricalbridging engagement with said resistance track and said conductingcollector track supported by the respective substrate elements; and

terminal connections for said respective resistance tracks and saidrespective collector tracks.

2. The variable resistance apparatus of claim 1, wherein said respectivebrushes are of triangular configuration and include three protrudingtoes each being located at the respective apices of each of saidbrushes, one of said toes being in sliding electrical contact with saidarcuate resistance track and the remaining toes being in slidingelectrical contact with said collector track. 1

3. The variable resistance apparatus of claim 1, wherein each of thebrush-receiving cavities are triangularly shaped and disposed with onapex positioned for rotational alignment with its respective arcuateresistance track and said one apex being further configured at itsterminus to define planar wall surfaces lying in angular intersectingplanes, said wall surfaces being normal to said respective resistancetrack, and said respective brushes being triangularly shaped and seatedin a respective cavity with one apex being arcuately configured and inlinear engagement with each of the respective said planar wall surfacesof said one apex of said cavity.

4. The variable resistance apparatus of claim 1, wherein the distal endsurface of the shaft-supported brush carrier includes a protrudingportion spaced from said arcuate resistance track to prevent the saidend surface from wiping against said track during rotation of saidshaft.

5. The variable resistance apparatus of claim 3, wherein the inner backsurface of each of the respective brushes is angularly disposed relativeto the plane intersecting the end of said brushes in electricallybridging engagement with said tracks, and wherein the biasing meanscomprises an elongated spring disposed transversely of and pressingagainst said angularly disposed back surface to provide a resultantforce acting to concurrently force the respective brush in a directioninto engagement with its respective resistance track and to force saidarcuately formed apex of said brush into said linear engagement withsaid planar wall surfaces of said cavity.

6. In a variable resistance apparatus comprising:

a housing;

a stationary insulating substrate element supported by said housing andincluding an interiorly facing surface supporting an arcuate resistancetrack and a conducting collector track;

a rotatable shaft extending inwardly of said housing and supporting atits inner end a contact brush carrier;

the combination therewith of;

triangularly shaped, brush-receiving cavities in said brush carrier anddisposed with one apex thereof positioned for rotational alignment withthe said arcuate resistance track, and said one apex being furtherconfigured at its terminus to define planar wall surfaces lying inangular intersecting planes, said wall surfaces being substantiallynormal to the surface of said substrate element supporting saidresistance track;

a conducting brush seated in said cavity and having an exposed surfacein slidably electrically bridging engagement with said tracks, saidbrush being triangularly shaped with one apex being arcuately configuredand in linear engagement with each of the respective planar wallsurfaces of said one apex of said cavity; and

biasing means disposed in said cavity intermediate the inner end of saidcavity and said brush, to thereby bias said brush into electricalbridging engagement with said tracks.

7. ln the variable resistance apparatus of claim 6, the inner backsurface of said'brush being angularly disposed relative to the planeintersectingthe end of said brush in electrically bridging engagementwith said tracks, and wherein the said biasing means comprises anelongated spring disposed transversely of and pressing against saidangularly disposed back surface of said brush to provide a resultantforce acting to concurrently force the brush in a direction towardsengagement with said tracks and to force said arcuately formed apex ofsaid brush into said linear engagement with said planar wall surface ofsaid cavity.

1. A variable resistance apparatus comprising: a housing; a pair ofspaced-apart, stationary insulating substrate element supported by saidhousing, at least one of which includes a shaft-receiving aperture; anarcuate resistance track and a conducting collector track supported byeach of said substrate elements and in respective facing relationship; arotatable shaft received in the apertured substrate element andextending inwardly of said housing; an integrally formed insulatedcontact brush carrier supported on the inner end of said rotatable shaftand positioned intermediate said resistance elements, said contact brushcarrier containing a pair of reentrant brush-receiving cavities onopposite sides thereof and disposed angularly relative to one another,the open ends of said cavities facing respective resistance tracks andcollector tracks supported by the respective substrate elements, thesaid reentrant cavities of said brush carrier each having a depthexceeding one-half the axial length of said brush carrier; conductingcontact brushes disposed on opposite sides of said contact carrier andpositioned in the respective cavities of said contact brush carrier andslidably electrically bridging the respective facing resistance andcollector tracks; biasing means at opposite sides of said contactcarrier disposed in said respective cavities intermediate a respectiveinner end of said cavities and its respective brush, thereby biasingsaid brush into electrical bridging engagement with said resistancetrack and said conducting collector track supported by the respectivesubstrate elements; and terminal connections for said respectiveresistance tracks and said respective collector tracks.
 2. The variableresistance apparatus of claim 1, wherein said respective brushes are oftriangular configuration and include three protruding toes each beinglocated at the respective apices of each of said brushes, one of saidtoes being in sliding electrical contact with said arcuate resistancetrack and the remaining toes being in sliding electrical contact withsaid collector track.
 3. The variable resistance apparatus of claim 1,wherein each of the brush-receiving cavities are triangularly shaped anddisposed with on apex positioned for rotational alignment with itsrespective arcuate resistance track anD said one apex being furtherconfigured at its terminus to define planar wall surfaces lying inangular intersecting planes, said wall surfaces being normal to saidrespective resistance track, and said respective brushes beingtriangularly shaped and seated in a respective cavity with one apexbeing arcuately configured and in linear engagement with each of therespective said planar wall surfaces of said one apex of said cavity. 4.The variable resistance apparatus of claim 1, wherein the distal endsurface of the shaft-supported brush carrier includes a protrudingportion spaced from said arcuate resistance track to prevent the saidend surface from wiping against said track during rotation of saidshaft.
 5. The variable resistance apparatus of claim 3, wherein theinner back surface of each of the respective brushes is angularlydisposed relative to the plane intersecting the end of said brushes inelectrically bridging engagement with said tracks, and wherein thebiasing means comprises an elongated spring disposed transversely of andpressing against said angularly disposed back surface to provide aresultant force acting to concurrently force the respective brush in adirection into engagement with its respective resistance track and toforce said arcuately formed apex of said brush into said linearengagement with said planar wall surfaces of said cavity.
 6. In avariable resistance apparatus comprising: a housing; a stationaryinsulating substrate element supported by said housing and including aninteriorly facing surface supporting an arcuate resistance track and aconducting collector track; a rotatable shaft extending inwardly of saidhousing and supporting at its inner end a contact brush carrier; thecombination therewith of; triangularly shaped, brush-receiving cavitiesin said brush carrier and disposed with one apex thereof positioned forrotational alignment with the said arcuate resistance track, and saidone apex being further configured at its terminus to define planar wallsurfaces lying in angular intersecting planes, said wall surfaces beingsubstantially normal to the surface of said substrate element supportingsaid resistance track; a conducting brush seated in said cavity andhaving an exposed surface in slidably electrically bridging engagementwith said tracks, said brush being triangularly shaped with one apexbeing arcuately configured and in linear engagement with each of therespective planar wall surfaces of said one apex of said cavity; andbiasing means disposed in said cavity intermediate the inner end of saidcavity and said brush, to thereby bias said brush into electricalbridging engagement with said tracks.
 7. In the variable resistanceapparatus of claim 6, the inner back surface of said brush beingangularly disposed relative to the plane intersecting the end of saidbrush in electrically bridging engagement with said tracks, and whereinthe said biasing means comprises an elongated spring disposedtransversely of and pressing against said angularly disposed backsurface of said brush to provide a resultant force acting toconcurrently force the brush in a direction towards engagement with saidtracks and to force said arcuately formed apex of said brush into saidlinear engagement with said planar wall surface of said cavity.